Micro-machined absolute pressure sensor
First Claim
1. An absolute pressure sensor, comprising:
- a semiconductor membrane having a welled portion and a substantially planar peripheral surface surrounding and connected to the welled portion;
a pad of substantially nonconductive material formed directly on a portion of the peripheral surface of the semiconductor membrane;
a bonding layer deposited on the peripheral surface and the nonconductive pad so as to completely surround the welled portion of the semiconductor membrane;
a generally planar nonconductive base having an upper surface with spaced apart first and second metal conductors deposited thereon, the upper surface of the nonconductive base being brought into contact with a lower surface of the bonding layer and bonded to the semiconductor membrane in a vacuum so as to form a peripheral seal and a vacuum-sealed reference cavity adjacent the welled portion of the semiconductor membrane;
the first conductor includes a capacitor plate disposed within the vacuum-sealed reference cavity and an externally accessible lead attached to the capacitor plate and extending continuously and contiguously along the upper surface of the base through the peripheral seal;
the second conductor being in electrical communication with the semiconductor membrane; and
the first conductor being electrically isolated from the semiconductor membrane by the pad of substantially nonconductive material.
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Accused Products
Abstract
A micro-machined absolute pressure sensor and process for making the same. A semiconductor membrane having a welled portion connected to a planar periphery is formed in recess in a silicon substrate through etching and boron diffusion. A dielectric pad is formed on a portion of the planar periphery, and a bonding layer of polysilicon or amorphous silicon is deposited over the semiconductor membrane and the dielectric pad. After an etching process that defines the outline of the semiconductor membrane, the bonding layer is bonded to a nonconductive substrate in a vacuum using electrostatic bonding or wafer bonding, forming a vacuum-sealed reference cavity. A first and a second conductor are disposed on an upper surface of the nonconductive substrate. The first conductor serves as a capacitor plate disposed within the reference cavity and is connected to a transfer lead that passes from the cavity. The transfer lead is electrically isolated from the semiconductor membrane by the dielectric pad. The second conductor is electrically connected to the semiconductor membrane. The semiconductor membrane and the capacitor plate store an electrical charge that varies as a function of the distance between the capacitor plate and the semiconductor membrane. The semiconductor membrane flexes in response to pressure, changing the capacitance and the charge, so as to indicate the pressure of external fluid acting on the semiconductor membrane.
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Citations
13 Claims
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1. An absolute pressure sensor, comprising:
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a semiconductor membrane having a welled portion and a substantially planar peripheral surface surrounding and connected to the welled portion;
a pad of substantially nonconductive material formed directly on a portion of the peripheral surface of the semiconductor membrane;
a bonding layer deposited on the peripheral surface and the nonconductive pad so as to completely surround the welled portion of the semiconductor membrane;
a generally planar nonconductive base having an upper surface with spaced apart first and second metal conductors deposited thereon, the upper surface of the nonconductive base being brought into contact with a lower surface of the bonding layer and bonded to the semiconductor membrane in a vacuum so as to form a peripheral seal and a vacuum-sealed reference cavity adjacent the welled portion of the semiconductor membrane;
the first conductor includes a capacitor plate disposed within the vacuum-sealed reference cavity and an externally accessible lead attached to the capacitor plate and extending continuously and contiguously along the upper surface of the base through the peripheral seal;
the second conductor being in electrical communication with the semiconductor membrane; and
the first conductor being electrically isolated from the semiconductor membrane by the pad of substantially nonconductive material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An absolute pressure sensor, comprising:
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a semiconductor membrane having a welled portion and a substantially planar peripheral surface surrounding and connected to the welled portion;
a pad of substantially nonconductive material formed directly on a portion of the peripheral surface of the semiconductor membrane;
a bonding layer deposited on the peripheral surface and the nonconductive pad so as to completely surround the welled portion of the semiconductor membrane;
a generally planar nonconductive silicon base having an upper surface with spaced apart first and second metal conductors deposited thereon, the upper surface of the nonconductive base being brought into contact with a lower surface of the bonding layer and bonded to the semiconductor membrane in a vacuum so as to form a peripheral seal and a vacuum-sealed reference cavity adjacent the welled portion of the semiconductor membrane;
the first conductor includes a capacitor plate disposed within the vacuum-sealed reference cavity and an externally accessible lead attached to the capacitor plate and extending continuously and contiguously along the upper surface of the base through the peripheral seal;
the second conductor being in electrical communication with the semiconductor membrane;
the first conductor being electrically isolated from the semiconductor membrane by the pad of substantially nonconductive material; and
the substantially nonconductive pad having a non-annular cross-section in a plane parallel to the base such that the pad extends less than fully around the peripheral seal.
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Specification